Bug fix: Fixed a bug where the knobs layout was incorrect
Bug fix: never return a reference to a mutex-protected member!!
can the renderFormat be empty? Please explain
an empty ROD is not a failure
update openfx
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Global/GitVersion.h
more asserts on image size
add another null-rod assert
Add tooltips
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Global/GitVersion.h
avoid having references to mutex-protected Format object. Passing arguments by reference solves this
fix warnings
Bug fixes:

- A disabled combo box will have its label set black
- Any disabled knob will have its label set black
- It is now possible to disable group parameters (see OFX KitchenSink)
- Fixed a bug in the VideoEngine where the hash computation wasn't done
when we were changing the tree.
- Fixed the null render format (it wasn't initialised always)
- A cached image whose RoD is the project format will have its RoD
checked against the current project format before considering it as a
valid image.
Git version & update OpenFX
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Engine/EffectInstance.cpp
	Engine/EffectInstance.h
	Engine/Node.cpp
	Engine/Node.h
	Engine/OfxEffectInstance.cpp
	Engine/OfxParamInstance.cpp
	Engine/ViewerInstance.cpp
	Gui/ViewerGL.cpp
Histogram: fix static analysis error + format see Chapter 3 of https://www.kernel.org/doc/Documentation/CodingStyle

Linux coding style rules
HistogramCPU: free() works on a NULL pointer too!
Bug fix:

- Revert all code in ViewerInstance, recursive cache find and maybe a
getRegionOfDefinition call is potentially much cheaper than calling
getImage() which might call render
-  Fix the assert in Image.h and explain why
Don't decrement the age when doing undo/redo, this is wrong, just keep
incrementing.
Bug fix + optimization:

- A curve with the last keyframe whose right derivative is 0 was not
always drawn correctly
- Optimisation of the code in renderViewer so when an image is not
cached we do not call getRegionOfDefinition twice.